1. Field of the Invention
This invention relates to a refrigerating circuit used for cooling a vehicle, and more particularly, to a method of defrosting the refrigerating circuit.
2. Description of the Prior Art
With reference to FIG. 1, a refrigerating circuit 10 generally used for cooling a vehicle is schematically shown. Refrigerating circuit 10 includes compressor 11, condenser 12 and cooling unit 13 disposed within the environs of a vehicle to be cooled (not shown). Of course, the vehicle to be cooled may be an automobile, a truck, a bus, a plane or other mobile apparatus having a passenger or other compartment to be cooled. Compressor 11 is providing with electromagnetic clutch 111 for intermittently transferring the dynamic power of an engine (not shown) of the vehicle to compressor 11. Cooling unit 13 comprises evaporator 131, evaporator motor fan 132, and a casing disposing evaporator 131 therewithin (symbolically shown by a broken line). Conduits 14, 15, 16 normally connect compressor 11 and condenser 12, condenser 12 and evaporator 131, and evaporator 131 and compressor 11 respectively. Condenser 12 condenses refrigerant gas discharged from compressor 11. Condenser motor fan 121 is disposed near condenser 12 and makes air outside of the vehicle pass through condenser 12. Expansion valve 17 is disposed between condenser 12 and evaporator 131 in conduit 15 and expands condensed refrigerant flowing from condenser 12. Evaporator motor fan 132 is disposed near evaporator 131 and causes air in the vehicular chamber to be cooled to pass through evaporator 131. Consequently, the vehicular chamber is cooled. Bypass conduit 18 connects conduit 14 and that portion of conduit 15 located between expansion valve 17 and evaporator 131. Solenoid valve 19 located in bypass conduit 18 selectively bypasses the refrigerant gas discharged from compressor 11 directly to evaporator 131.
According to the prior art, defrosting a frost formed at cooling unit 13 is carried out via bypass conduit 18. When a refrigerating control apparatus (not shown) including a defrosting control system receives a signal requesting a defrosting of a frost formed at cooling unit 13, refrigerant gas discharged from compressor 11 is directly bypassed to evaporator 131 by operation of solenoid valve 19. Bypassing discharged refrigerant gas to evaporator 131 is continued until a predetermined period of time has lapsed. When the predetermined period of time elapses, refrigerant gas flows again into condenser 12 by operation of solenoid valve 19. Accordingly, defrosting a frost formed at cooling unit 13 is terminated and cooling of the vehicular chamber begins again.
Furthermore, in another known type of defrosting control system, defrosting a frost formed at cooling unit 13 is terminated when the temperature of an outer surface of evaporator 131 increases to a predetermined value.
However, according to the above-mentioned prior art method, each frost formed at the evaporator 131, the motor fan 132, the casing and a drain pipe for the casing are defrosted only by leading discharged refrigerant gas into the evaporator so that the time which has elapsed of leading discharged refrigerant gas into the evaporator may be prolonged. Accordingly, remarkably raising a temperature in the vehicular chamber to be cooled causes an inferior cooling down characteristic of the cooling unit of the vehicular chamber. Furthermore, the durability of the compressor is reduced by compressing the discharged refrigerant gas over prolonged period.